ANALYSIS OF THE STRUCTURE AND SUBCELLULAR LOCATION OF FILAMENTOUS PHAGE-PIV

The gene IV protein of filamentous bacteriophages is an integral membr ane protein required for phage assembly and export. A series of gene I V=phoA fusion, gene IV deletion, and gene IV missense mutations have b een isolated and characterized. The alkaline phosphatase activity of t he fusion proteins suggests that pIV lacks a cytoplasmic domain. Cell fractionation studies indicate that the carboxy-terminal half of pIV m ediates its assembly into the membrane, although there is no single, d iscrete membrane localization domain. The properties of gene IV missen se and deletion mutants, combined with an analysis of the similarities between pIVs from various filamentous phage and related bacterial exp ort-mediating proteins, suggest that the amino-terminal half of pIV co nsists of a periplasmic substrate-binding domain that confers specific ity to the assembly-export system.